Chuck Harris wrote:
Hi Tim,

That is a common 475 problem. They have an electrostatic lens built
into the CRT to give it a large beam deflection with a very small change
in vertical plate amplitude. They use a very high anode voltage to give
you that nice bright trace at high sweep speeds.

Anyway, Tek used wire that has poor insulation for the 21KV anode lead.
The lead is potted right into the tube's anode terminal. Clean up all
the black gook that the anode lead sucked out of the air with isopropyl
alcohol (91%), and coat the offending section of the anode lead with
a good grade of clear silicone RTV...preferably the kind that doesn't
smell like vinegar. [...]

The kind that doesn't release acetic acid on curing is usually labelled
"Silicone II" on the tube.

Cheers,
Fred
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